How to distinguish poison sumac from tree of heaven
I cannot distinguish between poison sumac and the beginnings of the invasive "Tree of Heaven". I am trying to avoid the terrible outbreak of poison blisters [ivy, sumac, or oak], that caused me to miss an entire week of work. I am not sure which poison I had but I certainly was pulling lots of "Trees of Heaven" out of bushes and flower beds one weekend. They look alot like poison sumac...even have red stems. See attached pictures.
It is actually likely that you inadvertently contacted poison ivy, which is a weedy vine that would also inhabit the areas that are shown in your photos.
Poison oak, and "Poison sumac" are found in areas that are incredibly marshy and wet, and are found on the Eastern Shore of Maryland. Though many of us grew up calling a plant 'Poison sumac" , it wasn't a sumac (Rhus) at all and it's scientific name has been changed to reflect that- Toxicodendron vernix. It has white hairless fruit, hairless stems and round, smooth (entire) leaf edges.
Take a look here: http://www.poison-ivy.org/poison-sumac
We can say that because both plants in your photos show serrated leaf edges, they are not poison sumac. To confuse things further, there are multiple types of real sumac (Rhus family).
Tree of Heaven has smooth leaf edges except for one or two notches at the base of the leaf. It has red stems, but the biggest way to check is to take a piece of the leaf, crush it and smell it. It stinks like rotten peanut butter. In fact, another name used for this plant in the past was 'stinking sumac'.
Additionally, walnut seedlings also look like these plants. We wonder if your first photo is that.
Here is another page that helps you to know Poison Ivy, which grows everywhere in Frederick County:
http://extension.umd.edu/hgic/poison-ivy Be sure to click on the link to the full publication, HG34 which has lots of good information, including common myths on how it spreads.
The bottom line is, protect yourself well if you are working in overgrown areas- long sleeves, gloves etc., or hire someone to do the work for you.